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Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" From: @(#)inet.4 8.1 (Berkeley) 6/5/93 33.\" $FreeBSD$ 34.\" 35.Dd February 14, 1995 36.Dt INET 4 37.Os 38.Sh NAME 39.Nm inet 40.Nd Internet protocol family 41.Sh SYNOPSIS 42.In sys/types.h 43.In netinet/in.h 44.Sh DESCRIPTION 45The Internet protocol family is a collection of protocols 46layered atop the 47.Em Internet Protocol 48.Pq Tn IP 49transport layer, and utilizing the Internet address format. 50The Internet family provides protocol support for the 51.Dv SOCK_STREAM , SOCK_DGRAM , 52and 53.Dv SOCK_RAW 54socket types; the 55.Dv SOCK_RAW 56interface provides access to the 57.Tn IP 58protocol. 59.Sh ADDRESSING 60Internet addresses are four byte quantities, stored in 61network standard format (on the 62.Tn VAX 63these are word and byte 64reversed). 65The include file 66.In netinet/in.h 67defines this address 68as a discriminated union. 69.Pp 70Sockets bound to the Internet protocol family utilize 71the following addressing structure, 72.Bd -literal -offset indent 73struct sockaddr_in { 74 uint8_t sin_len; 75 sa_family_t sin_family; 76 in_port_t sin_port; 77 struct in_addr sin_addr; 78 char sin_zero[8]; 79}; 80.Ed 81.Pp 82Sockets may be created with the local address 83.Dv INADDR_ANY 84to affect 85.Dq wildcard 86matching on incoming messages. 87The address in a 88.Xr connect 2 89or 90.Xr sendto 2 91call may be given as 92.Dv INADDR_ANY 93to mean 94.Dq this host . 95The distinguished address 96.Dv INADDR_BROADCAST 97is allowed as a shorthand for the broadcast address on the primary 98network if the first network configured supports broadcast. 99.Sh PROTOCOLS 100The Internet protocol family is comprised of 101the 102.Tn IP 103network protocol, Internet Control 104Message Protocol 105.Pq Tn ICMP , 106Internet Group Management Protocol 107.Pq Tn IGMP , 108Transmission Control 109Protocol 110.Pq Tn TCP , 111and User Datagram Protocol 112.Pq Tn UDP . 113.Tn TCP 114is used to support the 115.Dv SOCK_STREAM 116abstraction while 117.Tn UDP 118is used to support the 119.Dv SOCK_DGRAM 120abstraction. 121A raw interface to 122.Tn IP 123is available 124by creating an Internet socket of type 125.Dv SOCK_RAW . 126The 127.Tn ICMP 128message protocol is accessible from a raw socket. 129.Pp 130The 32-bit Internet address contains both network and host parts. 131However, direct examination of addresses is discouraged. 132For those 133programs which absolutely need to break addresses into their component 134parts, the following 135.Xr ioctl 2 136commands are provided for a datagram socket in the Internet domain; 137they have the same form as the 138.Dv SIOCIFADDR 139command (see 140.Xr intro 4 ) . 141.Pp 142.Bl -tag -width SIOCSIFNETMASK 143.It Dv SIOCSIFNETMASK 144Set interface network mask. 145The network mask defines the network part of the address; 146if it contains more of the address than the address type would indicate, 147then subnets are in use. 148.It Dv SIOCGIFNETMASK 149Get interface network mask. 150.El 151.Sh ROUTING 152The current implementation of Internet protocols includes some routing-table 153adaptations to provide enhanced caching of certain end-to-end 154information necessary for Transaction TCP and Path MTU Discovery. 155The 156following changes are the most significant: 157.Bl -enum 158.It 159All IP routes, except those with the 160.Dv RTF_CLONING 161flag and those to multicast destinations, have the 162.Dv RTF_PRCLONING 163flag forcibly enabled (they are thus said to be 164.Dq "protocol cloning" ) . 165.It 166When the last reference to an IP route is dropped, the route is 167examined to determine if it was created by cloning such a route. 168If this is the case, the 169.Dv RTF_PROTO3 170flag is turned on, and the expiration timer is initialized to go off 171in net.inet.ip.rtexpire seconds. 172If such a route is re-referenced, 173the flag and expiration timer are reset. 174.It 175A kernel timeout runs once every ten minutes, or sooner if there are 176soon-to-expire routes in the kernel routing table, and deletes the 177expired routes. 178.El 179.Pp 180A dynamic process is in place to modify the value of 181net.inet.ip.rtexpire if the number of cached routes grows too large. 182If after an expiration run there are still more than 183net.inet.ip.rtmaxcache unreferenced routes remaining, the rtexpire 184value is multiplied by 3/4, and any routes which have longer 185expiration times have those times adjusted. 186This process is damped somewhat by specification of a minimum rtexpire value 187(net.inet.ip.rtminexpire), and by restricting the reduction to once in 188a ten-minute period. 189.Pp 190If some external process deletes the original route from which a 191protocol-cloned route was generated, the 192.Dq child route 193is deleted. 194(This is actually a generic mechanism in the routing code support for 195protocol-requested cloning.) 196.Pp 197No attempt is made to manage routes which were not created by protocol 198cloning; these are assumed to be static, under the management of an 199external routing process, or under the management of a link layer 200(e.g., 201.Tn ARP 202for Ethernets). 203.Pp 204Only certain types of network activity will result in the cloning of a 205route using this mechanism. 206Specifically, those protocols (such as 207.Tn TCP 208and 209.Tn UDP ) 210which themselves cache a long-lasting reference to route for a destination 211will trigger the mechanism; whereas raw 212.Tn IP 213packets, whether locally-generated or forwarded, will not. 214.Ss MIB Variables 215A number of variables are implemented in the net.inet branch of the 216.Xr sysctl 3 217MIB. 218In addition to the variables supported by the transport protocols 219(for which the respective manual pages may be consulted), 220the following general variables are defined: 221.Bl -tag -width IPCTL_FASTFORWARDING 222.It Dv IPCTL_FORWARDING 223.Pq ip.forwarding 224Boolean: enable/disable forwarding of IP packets. 225Defaults to off. 226.It Dv IPCTL_FASTFORWARDING 227.Pq ip.fastforwarding 228Boolean: enable/disable the use of fast IP forwarding code. 229Defaults to off. 230When fast forwarding is enabled, IP packets are forwarded directly to 231the appropriate network interface with a minimal validity checking, which 232greatly improves the throughput. 233On the other hand, they bypass the 234standard procedures, such as IP option processing and 235.Xr ipfirewall 4 236checking. 237It is not guaranteed that every packet will be fast-forwarded. 238.It Dv IPCTL_SENDREDIRECTS 239.Pq ip.redirect 240Boolean: enable/disable sending of ICMP redirects in response to 241unforwardable 242.Tn IP 243packets. 244Defaults to on. 245.It Dv IPCTL_DEFTTL 246.Pq ip.ttl 247Integer: default time-to-live 248.Pq Dq TTL 249to use for outgoing 250.Tn IP 251packets. 252.It Dv IPCTL_ACCEPTSOURCEROUTE 253.Pq ip.accept_sourceroute 254Boolean: enable/disable accepting of source-routed IP packets (default false). 255.It Dv IPCTL_SOURCEROUTE 256.Pq ip.sourceroute 257Boolean: enable/disable forwarding of source-routed IP packets (default false). 258.It Dv IPCTL_RTEXPIRE 259.Pq ip.rtexpire 260Integer: lifetime in seconds of protocol-cloned 261.Tn IP 262routes after the last reference drops (default one hour). 263This value varies dynamically as described above. 264.It Dv IPCTL_RTMINEXPIRE 265.Pq ip.rtminexpire 266Integer: minimum value of ip.rtexpire (default ten seconds). 267This value has no effect on user modifications, but restricts the dynamic 268adaptation described above. 269.It Dv IPCTL_RTMAXCACHE 270.Pq ip.rtmaxcache 271Integer: trigger level of cached, unreferenced, protocol-cloned routes 272which initiates dynamic adaptation (default 128). 273.El 274.Sh SEE ALSO 275.Xr ioctl 2 , 276.Xr socket 2 , 277.Xr sysctl 3 , 278.Xr icmp 4 , 279.Xr intro 4 , 280.Xr ip 4 , 281.Xr ipfirewall 4 , 282.Xr tcp 4 , 283.Xr ttcp 4 , 284.Xr udp 4 285.Rs 286.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial" 287.%B PS1 288.%N 7 289.Re 290.Rs 291.%T "An Advanced 4.3 BSD Interprocess Communication Tutorial" 292.%B PS1 293.%N 8 294.Re 295.Sh CAVEAT 296The Internet protocol support is subject to change as 297the Internet protocols develop. Users should not depend 298on details of the current implementation, but rather 299the services exported. 300.Sh HISTORY 301The 302.Nm 303protocol interface appeared in 304.Bx 4.2 . 305The 306.Dq protocol cloning 307code appeared in 308.Fx 2.1 . 309